- Female golden rocket frogs prefer males with longer call lengths featuring more pulses, which correlates to their parental care abilities, researchers have found.
- Male removal experiments in Kaieteur National Park in Guyana revealed that hatching success is four times higher in clutches with attentive fathers than those without a father present.
- By honestly advertising their parental care abilities, male frogs can inform females of their potential to protect their eggs and tadpoles from desiccation and predation.
Rain drenched a team of ecologists in the Kaieteur National Park in Guyana as they scrambled to keep their sound equipment dry. They were recording a male golden rocket frog (Anomaloglossus beebei) chirping in a nearby bromeliad, getting close enough to prevent the low rumble of Kaieteur Falls from drowning out the 1.9-centimer-long (0.75-inch) amphibian. The minuscule male advertised for a female mate with a series of high-pitched peeps akin to an oven timer going off. Simultaneously, the ecologists believed, he conveyed his parenting skills to the discerning females.
When females of this rare species listen closely, it seems to improve the likelihood that their offspring will survive. In a recent study published in Behavioral Ecology, researchers showed that male golden rocket frogs with calls lasting just milliseconds longer are better parents to their eggs and tadpoles, increasing their hatching rates and keeping them safe from predators. Females prefer to mate with such fathers, the team found – the first evidence of “good parent” advertising in frogs.
These tiny neotropical frogs, an IUCN endangered species, are not found anywhere else in the world. Constant mist from the waterfalls and open glades of tropical flowering plants that collect pools of water provide an oasis for them, but recent mining expansion nearby poses a serious threat to their small habitat. For reasons scientists do not yet grasp, only the females are a bright golden yellow. Much more clear is the species’ special co-parenting arrangement: the mothers and fathers provide different types of care, with males playing an unusually extensive role. Males protect their eggs from drying out and, when threatened by predators, transport them between the pools of water formed in leaf axils for safety.
The blandly colored males rely on their distinctive vocal chops [audio clip] to attract females.
“I was curious to explore what kind of information the females might be able to gather via this call,” said Beth A. Pettitt, an ecologist from the University of Minnesota and lead author of the study. Specifically, she wanted to investigate whether females could gain insight about the potential quality of a male’s parental care through his “voiceprint” alone.
Her team visited the Guyana highlands for three-month spans in two consecutive years to get up close to the frogs during their peak breeding times. Following accepted guidelines for amphibian field research, the researchers removed 40 males from their egg clutches to test the impact of male care on hatching. When fathers were present, hatching success rose nearly four times higher, they found, though some offspring survived even with an absent father.
Pettit’s team also recorded 261 calls from 29 male frogs and observed their parental care behaviors. Attentive fathers spent more time within 30 centimeters (12 inches) of their eggs and tadpoles, and defended their territory from competitive males. They found that males with longer calls were among the more attentive fathers. On average, males with shorter calls spent less time with their eggs.
Finally, the ecologists re-played recordings of male calls for individual females to test their preferences. They altered several sonic properties of the calls: the pitch (or frequency), the rates (number of calls per minute) and the duration (number of pulses per call). Pitch and rates didn’t affect the females’ attention. However, they clearly preferred longer calls with more pulses — directly corresponding with the males’ attentiveness as fathers.
“Call duration was the only call trait we measured that females cared about at all,” said study co-author Mark Bee, also of the University of Minnesota. “It was an honest predictor of how much time males attended their developing embryos and defended the territories where their offspring were developing.”
The team concluded that golden rocket frog calls are a strong example of the “Good Parent Hypothesis,” which predicts that females select their mates based on an honest advertisement of parenting ability. It’s one of several competing scenarios for how mating calls work in the wild.
As for why calling and parental care might be linked, Pettit’s team says most parents can relate to the likely answer: energy. Raising their young and advertising via loud calls both require significant outputs of energy. Some frogs increase their oxygen consumption and metabolic rates by as much as 25 times during active calling periods, rivaling human athletes during a workout. “That’s really quite remarkable,” said Bee.
“I think this is a compelling example [of the good parent hypothesis],” said biologist James Tumulty of Cornell University in Ithaca, New York, who was not involved in the study. “Since calling is energetically expensive in frogs, I would interpret these results as females preferring males who are in better condition, and males in better condition may be able to do everything better.”
Biologist Eva Ringler of the Messerli Research Institute in Vienna, Austria, concurs. “It seems that indeed females select for honest traits [longer calls] that reflect male parental quality,” Ringler said. Given the generally low survival rates of the frogs’ egg clutches, she would like to see future studies to determine whether the females’ choices raise the reproductive success for the species long term.
Beth A Pettitt, Godfrey R Bourne, Mark A Bee, Females prefer the calls of better fathers in a Neotropical frog with biparental care, Behavioral Ecology, arz172, https://doi.org/10.1093/beheco/arz172
Lara Streiff (@LaraGStreiff) is a graduate student in the Science Communication Program at the University of California, Santa Cruz. Other Mongabay stories produced by UCSC students can be found at news.mongabay.com/list/ucsc.